A thermal tissue operation involves simultaneously compressing and heating tissue to seal together pieces of tissue, to cut a single piece of tissue into separate parts, or to sequentially seal pieces of tissue and then cut the sealed tissue. Tissue cutting occurs in the same manner as tissue sealing, except that additional energy and heat are applied to the tissue to cause it to sever. Typical thermal tissue operations involve sealing blood vessels during surgery to prevent bleeding and blood loss. Sealing a blood vessel before severing it between spaced apart sealed locations or in the middle of single sealed location completely avoids blood loss.
A thermal tissue operating system includes a handpiece which is connected to an energy source. The handpiece has a pair of opposing jaws between which the tissue is mechanically compressed. Electrical power from the energy source is converted to thermal heat energy in at least one of the opposing jaws, and the heat is conducted into the compressed tissue. The characteristics of the electrical energy applied to the jaws control the characteristics of the heat energy conducted into the jaws. The characteristics of the thermal energy transferred to the tissue and the time during which the thermal energy is transferred constitute an individual thermal tissue operation, i.e. a tissue sealing operation, a tissue cutting operation, or a combined tissue cutting and sealing operation. Usually, the entire surgical procedure is completed by performing many separate individual thermal tissue operations.
A thermal tissue operating system can be subject to a number of external influences, such as accidental mishandling and improper use, for example. Such external influences have the potential to adversely affect the proper operation of the system. A malfunctioning or improperly functioning system may inadequately seal tissue, inadequately cut tissue, inadequately seal and cut the tissue, and otherwise complicate the surgical procedure.
The jaw heating elements are subject to especially rigorous operating conditions. The jaw heating elements must conduct relatively high electrical current, must withstand rapidly increasing temperatures, must efficiently transfer thermal energy to the compressed tissue, and must maintain high temperature during the thermal tissue operation, among other things. When the thermal tissue operation is completed and electrical current is no longer conducted, the jaw heating elements undergo rapid cooling. The substantial changes in the electrical current conducted and the rapid increases and decreases in temperature impose significant stresses on the resistive material of the jaw heating elements and on the material surrounding the resistive material and on the adjoining structures and materials which support the jaw heating elements.
The cyclic nature of the energy application during repeated thermal tissue operations performed during the surgical procedure creates a practical limitation on the number of times that the heating elements will perform satisfactorily. For example, repeated use can cause the resistive material to undergo changes in properties or to develop areas of reduced or increased conductivity, resulting in changes in the resistance and thermal response characteristics of the jaw heating elements. As another example, an exaggerated temperature might melt the electrical connections to the jaw heating elements or even melt parts of the jaw heating elements or their supporting structures. Such adverse circumstances might cause an open circuit or short circuit condition to occur. Of course an open circuit prevents the jaw heating elements from conducting current and creating thermal energy. A short circuit might cause electrical current to flow into portions of the handpiece where it is not intended and could overload and therefore damage the energy source of the thermal tissue operating system.
A typical thermal tissue operating system employs feedback to regulate the amount of energy supplied to the jaw heating elements, thereby assuring that a desired temperature is applied or a desired amount of energy is transferred to the tissue compressed between the jaws. If the resistance of the jaw heating elements changes or if the current flow path to the heating elements changes in such a way to prevent or limit the maximum amount of current delivered to the jaw heating elements, the ability to regulate the temperature of the tissue compressed between the jaws will be impaired. Of course, impaired temperature regulation leads to degradation of the thermal tissue operation, because an insufficient or excessive amount of thermal energy will be applied to the compressed tissue.
In some cases where less than the desired amount of thermal energy is applied to the compressed tissue, it can be difficult or impossible for the surgeon to recognize that the thermal effect on the tissue is inadequate. For example, in the case of a vessel which carries blood or other body fluid, an attempt to seal the vessel with a moderately inadequate amount of thermal energy may create an effect which appears to the surgeon to be a sound tissue seal. The tissue effect may even withstand internal bodily blood or fluid pressure for some short amount of time, before beginning to leak or rupturing. The resulting internal bleeding or fluid loss will then require a resealing thermal tissue operation. If the resealing operation is performed during the course of the surgical procedure, the time to do so prolongs the entire surgical procedure and subjects the patient to additional trauma. If the internal bleeding or fluid loss is discovered after the initial surgical procedure has been completed, a second surgical procedure must be performed to gain access to the leak and seal it. Performing a second surgical procedure on the patient adds substantially to the trauma that the patient has already experienced.
It is desirable to identify potential problems with a thermal tissue operating system before it is used in the surgical procedure. The early identification of problems has the potential to avoid many significant subsequent complications. The invention of the above-referenced application Ser. No. 12/842,606 involves a number of self tests which the thermal tissue operating system performs on itself, preferably upon initial start-up or powering-on of the system. These self tests are very useful for identifying a number of different, potential problems which manifest themselves before the thermal tissue operating system is used during a surgical procedure. However, many of the initial start-up or power-on tests are performed only once before commencing a surgical procedure. The surgical procedure could continue for many hours, during which other problems might arise from repeated use of the thermal tissue operating system during the course of the surgical procedure.